Looking closer - here's a pic - it's filled with weeds too - more than grass in some areas. So the plan is some kind of week killer and fertilizer too I guess?

I have a ton of Miracle Grow Lawn Food (granulated sprayer type) so figured we would start with that...but really have no clue about this stuff.

BTW - We have well water and can water it all we like though it's the rain season right now and gets tons of water regularly...

It looks like you're mowing very low. It should be 3 inches. You can use end hose weed killer (make sure it is safe for st augustine!) that will get the job done quickly.

I don't know about Miracle Grow product but a cheap 15-5-10 or something similar should help get them fill in fast as long as you're mowing at 3 inches height.

Agree. Set your mower to the highest setting and weld it in place. It never needs to be lower than that. You're currently mowing at the lowest setting. That will let lots of weeds in.

When you do water, how often and how long do you water? Like if it rained today, when would you water again?

Read the label on the Miracle Gro and see if there are any temperature restrictions. If not then you can apply at the bag rate. In addition, I would get a 50-pound bag of alfalfa pellets and start using that for the rest of your time at that house. Why? Because you can use it to encourage new growth any time you want to. With chemical fertilizers you have to worry about overdoing it or applying in the sun/heat, or what happens if it rains before or after you apply. With the organic alfalfa pellets (rabbit chow) you don't have to worry about anything. Application rate is 20 pounds per 1,000 square feet. You can apply the same day as the Miracle Gro. The alfalfa will go to work right away but you will not see the improvement for 3 weeks. The Miracle Gro should green it up much faster, but it has those other issues if you're trying to speed up the process.